Phytotoxicity to maize increased with each successive increase in the dose of chlorsulfuron applied in wheat. Chlorsulfuron at 30 g ha_1 resulted in 49.0% toxicity to maize, which was significantly lower than toxicity under chlorsulfuron at 40 or 50 g ha_1. The toxicity at 20 g ha_1 was 29.3%. Consequently, the fodder yield of maize reduced with an increasing dose of chlorsulfuron applied in wheat. Chlorsulfuron at 20 and 30 g ha_1 caused 24 and 52% reduction in fodder yield of maize, as compared to untreated control. The reduction in yield further increased to the extent of 67 and 83%, where chlorsulfuron was applied at 40 and 50 g ha_1, respectively, in wheat. In order to achieve satisfactory weed control, chlorsulfuron at 20-30 g ha_1 could be applied in wheat, but maize should not be grown in rotation.
The winter wheat (Triticum aestivum L.) – maize
(Zea mays L.) fallow is a common rotation in the semiarid plains of
India, which receives 430 to 600 mm precipitation annually.
In India, there has been a tremendous increase in the use of herbicides in the recent
past, and at present, a vast variety of herbicides are available in the market for weed control
in different crops. The safe and continuous use of these herbicides would require
knowledge of their behavior in soil. Herbicides which decompose too rapidly are less adaptive
in some situations, as they cannot be effective on weeds emerging late in the season. On
the other hand, herbicides which have longer persistence are unsuitable, as their
residues can cause injury to the sensitive crops grown in rotation. Ideally, a herbicide
should therefore remain active enough to provide satisfactory weed control up to a critical
period of weed competition and then degrade to innocuous products before it is necessary
to apply it again. Therefore, it is important to know whether the herbicide applied to
soil would persist and or will disappear within a relatively short span of time.
Chlorsulfuron (Chlorsulfuron
1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea belonging to sulfonylurea group of herbicides, was evaluated
for selective control of broadleaf weeds in cereals like wheat
(Triticum aestivum), barley
(Hordeum vulgare) and wild oat (Avena
sativa) (James et al., 1999). The sulfonylureas
exhibit soil activity at extraordinarily low rates of application and residual weed control in
the range of 5-40 g ha_1 (Elftherohorinos, 1987; and Beyer et al., 1988). Such herbicides persist in soil for more than one growing season and may cause toxicity to rotational
crops (Petrerson and Arnold, 1985; Beyer et
al., 1988; Friesen and Wall, 1991; Kotoula-Syakaet al. 1993; and Moyer, 1995). Several researchers have reported injury to the
succeeding crop from chlorsulfuron residues in soil (Norris et al., 1981). Brewster and Appleby (1983) reported that soil residues of chlorsulfuron at 35 g
ha_1 injured snap bean (Phaseolus
vulgaris L.), alfa-alfa (Medicago
sativa L.), sweet corn (Zea mays L.), Italian rye grass
(Lolium multiflorum Lam), sugarbeet (Beta
vulgaris L.) and rape (Brassica napus L.). The half-life
of chlorsulfuron worldwide ranges from 2 to 13 months depending upon the soil and
climatic conditions (Beyer et al., 1988). Chlorsulfuron degradation is governed by edaphic
factors such as soil moisture and pH. The degradation rates of chlorsulfuron in soil follow
first order kinetics and are negatively correlated with pH and positively correlated
with temperature, soil moisture, organic matter content and microbial biomass in soil (Joshiet al., 1985; Thirunarayanan et al., 1985; and Streak, 1998). Results of studies conducted
in the US and European countries show that the half-life of chlorsulfuron varies from
14-168 days within a pH range of 5.2-8.2 (Sarmah et al., 1998). |
